Field of the Invention
The invention relates to a method and a device for operating an electromotive fan drive (fan) of a motor vehicle. A method in this case can be understood to mean, foe example, a control method for the speed control of a brushless electric motor of an electromotively driven fan of a motor vehicle by means of a closed-loop or open-loop device, the motor being connected to an on-board system voltage. A fan can be understood to mean, for example, a so-called HVAC fan (HVAC=Heating, Ventilation, and Air Conditioning) or a radiator cooling fan of the motor vehicle, especially of a heating and/or climate control fan drive.
Description of the Background Art
Closed-loop speed controls of fan and/or ventilator motors, used in a motor vehicle and exposed to the effect of fluctuating operating voltages, and corresponding closed-loop or open-loop control circuits are known, for example, from DE 44 08 442 A1, from DE 44 44 810 A1, from DE 198 55 424 A1, and from DE 10 2010 048 747 A1. The known open-loop or closed-loop control methods are based substantially on a change in the pulse duty factor of semiconductor switches, controlled by means of pulse width modulation (PWM), in the load circuit of the electric motor of an electromotive fan drive as a function of a fluctuating operating or on-board system voltage.
Because of the closed-loop control of the speed of such an electric motor or electromotive fan drive, in particular at a maximum or hundred percent modulation of the closed-loop speed control, speed oscillations can occur as is known, when the on-board electrical system, particularly an on-board system voltage and/or an on-board system current, of the motor vehicle fluctuates. Such oscillations in the on-board electrical system can also be desirable in relation to operation or usage or be required, for example, for the recuperation of the vehicle battery. In this case, for example, voltage variation gradients of 3 V/s at desired generator voltages of a maximum of 15.5 V and a minimum of 12 V can occur.
Such oscillations are acoustically perceptible, therefore audible, in the fan airflow. It is frequently necessary, therefore, accordingly to overdesign the electric motor in order to provide or make available actuating reserves. A further aspect is that the maximum achievable speed of an HVAC system depends on one or more flap positions of a climate control device; therefore, it is load-dependent and cannot be limited to a fixed value. Other operating conditions in the vehicle can also be the cause of load variations or load changes. Therefore, the employed drive motor can be accordingly cost-intensive and/or a maximum airflow (100% airflow) cannot be utilized in the vehicle.
The disadvantages are expected particularly in a brush motor and/or a brushless DC motor, which simulates a brush motor, because due to the system it must have a suitable actuating reserve. The so-called direct current or DC emulation (reproduction of the DC characteristic) means that the arising motor speed based on a set point predefined by an operating unit decreases with an increasing motor current.